Differential



Sept. 9, 1958 Filed Dec. 24, 1956 E. .WILDHABER DIFFERENTIAL '4 Sheets-Sheet 1 INVEN'IIOR} 5. WI LDHABER iii;

P 9,1958 E. WILDHABER 2,850,919

DIFFERENTIAL Filed Dec. 24, 1956 4 Sheets-Sheet. 2

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DIFFERENTIAL Filed Dec. 24, 1956 4 Sheets-Sheet 4 5O E. l /VILDHABERF1620 FlG.2/.

United States Patent Ufifice 2,850,919 Patented Sept. 9, 1958DIFFERENTIAL Ernest Wildhaber, Brighton, N. Y.

Application December 24, 1956, Serial No. 630,153

23 Claims. (Cl. 74-650) The present invention relates to differentials,and more particularly to differentials for use on automotive vehiclesfor connecting the two wheels of an axle, and for use between axles. Ina more specific aspect, the invention relates to cam-type differentialsof the axially acting type. 7

Such differentials generally comprise a pair of coaxial side membershaving tooth-like projections, and a driving member coaxial therewithand containing blocks adapted to slide axially therein and to engagesaid projections.

Differentials of the kind referred to can be designed with a partial, oreven complete, locking effect, so that loss of full traction on one ofthe driven wheels, for instance, of the vehicle leaves the other drivenwheel with a multiple of the decreased traction of said one wheel; andthe two driven wheels can still move with respect to each other, asrequired.

One object of the present invention is to provide a differential of thecharacter described in which the interengaging projections of the sidemembers and the sliding blocks have improved contact, so that thestresses at the contacting surfaces are reduced, with resulting increasein life, or load capacity, of the differential.

Another object of the invention is to attain this improved contact whileachieving smooth motion of the blocks.

A further object of the invention is to provide a differential in whichsurface contact is obtained between the side members and blocks.

A further, and important, object of the invention is to provide adifferential in which the side members and the blocks have projectionsor teeth that give a smaller end thrust at a given frictional brakingtorque, or locking effect, than known designs.

A related object of the invention is to provide a differential of thecharacter described in which the blocks have spirally-arranged teeth attheir ends for engagement with corresponding spirally-arranged teeth, onthe side members of the differential, and in which the hand of the teethis so selected that the resultant loads exerted at opposite sides ofeach block are contained approximately in a plane.

Another object of the invention is to provide a differential of thecharacter described in which the side members and the blocks haveprojections or teeth that can be produced with form tools, therebysimplifying their production.

To this end, a further aim of the invention is to provide a differentialof the character described in which the of the side members, forinstance, can be faced with a material of less strength than hardenedsteel, and that has improved friction characteristics.

A still further object of the invention is to provide a differential ofthe sliding block type having improved smoothness of operation.

Other objects of the invention will be apparent hereinafter from thespecification and from the recital of the appended claims.

In the drawings:

Fig. 1 is an axial section of a differential constructed according toone embodiment of this invention;

Fig. 2 is a section taken on the line 22 of Fig. 1, looking in thedirection of the arrows;

Fig. 3 is a fragmentary end view of a slightly modified form of drivingmember such as might be used in the differential of Fig. 1;

Fig. 4 is a fragmentary end view of a driving member of still anotherslightly modified form;

Fig. 5 is a diagram showing the preferred motion of the sliding blocksused in my differential, in terms of the relative turning displacementof a side member;

Fig. 6 is a fragmentary radial view of a side member and cooperatingabutment portion of a sliding block constructed with radial teethaccording to one embodiment of the present invention;

Fig. 7 is a fragmentary view similar to Fig. 6, but constructedaccording to another and preferred embodiment of the invention where theside members have spiral teeth;

Fig. 8 is a fragmentary view of the interengaging teeth of the membersof Fig. 7 in a position of full depth engagement;

Figs. 9 and 10 are end views of the two opposite side members,respectively, of the differential such as shown in Fig. 1, looking atthe toothed sides, and on a slightly smaller scale than Fig. 1;

Fig. 11 is a fragmentary end view looking at one end of the slidingblocks that are adapted to engage the teeth of the side members shown inFigs. 9 and 10;

Fig. 12 is an end view of the opposite ends of these sliding blocks;

Fig. 13 is a fragmentary view similar to Fig. 11, but illustrating aslightly modified embodiment of the sliding blocks;

Fig. 14 is a fragmentary section taken on the line of Fig. 9 from theoutside of the side member to the point of tangency 70 of the line 71 tothe base circle of the involutes along which the teeth are curvedlongitudinally;

Fig. 15 is a somewhat diagrammatic view looking radially outwardly atthe cylindrical inner ends of the teeth of the side members and of thecooperating sliding blocks, the view being developed into a plane, andthe figure showing slightly more than half the circumference at saidinner ends;

Fig. 16 is a diagrammatic view, similar to Fig. 15, but illustrating amodification of the sliding blocks;

Fig. 17 is a diagrammatic view, similar to Fig. 15, but showing afurther modification;

Fig. 18 is a fragmentary section taken in the peripheral directionthrough the middle of a spiral tooth of a side member, and showingdiagrammatically the direction of pressure exerted on that tooth;

Fig. 19 is afragmentary normal section taken through the middle of aspiral tooth at right angles to the lengthwise direction of that toothand showing a modified construction;

Fig. 20 is a view illustrating one way of producing the teeth of a sidemember, the side member being shown in section on a line tangent to thebase circle of the teeth;

Fig. 21 is a View of another form of tool that may be employed incutting the teeth of the side members, the view looking at the cuttingface of this tool;

Fig. 22 is a section, similar to Fig. 20, illustrating how a side membermay be cut with another form of tool; and

Fig. 23 is a section taken at right angles to Fig. 22 and in thelengthwise direction of the teeth being out, further illustrating thecutting process with the tool shown.

The differential of the present invention may be used as a power dividerbetween pairs of driven wheels of an automotive vehicle, or also as apower'divider between the two driven wheels of an axle; and it maybeused in other installations, also, wherever a differential is required.

The embodiment illustrated in Fig. l by way of example is a differentialfor driving the two wheels of an axle. The differential, indicatedgenerally at 30, comprises a centrally disposed driving member 31 whichis rigid with a drive gear 32. The drive gear is here shown as a helicalgear; but for passenger cars and light trucks a hypoid gear or othergear might be substituted for the helical drive gear shown. Gear 32receives power in known manner from a helical pinion, not shown, that isoperatively connected with a source of power.

Two end parts 33 and 34 are rigidly secured to the driving member 31 asby means of bolts 35 and nuts 36. They have seats 37 for suitableanti-friction hearings indicated diagrammatically in dotted lines at 38.Thus, the driving member 31 and the end parts 33, 34 form a rigid unitrotatably mounted in the bearings 38.

The driving member 31 is formed internally with straight axial grooves40 (Fig. 2). These grooves are of circular arcuate-profile, as denotedat 41. Sliding blocks 42 are movable in said grooves in the direction ofthe axis 43 of the differential. To save weight, the sliding blocks arerecessed as denoted at 44. At their radially inner ends the blocks 42bear against the cylindrical outside surfaceof a spacer ring 45 that iscentered by the sliding blocks, At their two axially opposite ends, theblocks 42 contain tooth-like projections 46, 47 (Fig. 1) which areadapted to engage other tooth-like projections 48, 49 provided on twoside members 50, 51. The sliding blocks 42 preferably have smallclearance 52 (Fig. 2) relative to each other.

The driving torque passes through the contacting projections of thesliding blocks and slide members. When the vehicle driven thereby movesin a straight path, the blocks are stationary in their grooves or ways40 and the side members 50, 51 move together, without relative motion.When the vehicle turns a corner, however, the wheels move relative toeach other, as do the two side members 50, 51; and as a result thesliding blocks reciprocate in the ways 40. The side members 50, 51 havesplined connection with the axle shafts 53, 53, respec tively, on whichthe two wheels of the vehicle are mounted.

Differentials having sliding blocks for connecting the two side membersof the differential are known. The present invention resides'chiefly inthe shape and arrangement of the teeth of the tooth like projections 46,47, 48, 49, of the sliding blocks and side members.

In the embodiment of the invention shown in Figs. l and 2, the ways 40for the sliding blocks are arcuate in shape. Figs. 3 and 4 illustratemodified shapes of ways for guiding the sliding blocks. In Fig. 3, thedriving member 31' is providedwith a plurality of cylindrical holes 54arranged in a circle about the axis 43 of the differential, that is,about the axis of the gear 31 and of the side members 50, 51. In thiscase, the sliding blocks are cylindrical in shape and reciprocate in thecylindrical axial guideways 54.

In Fig. 4, the driving member 31 of the differential has slots 55extending axially therethrough whose opposite sides are planes parallelto an axial plane of the differential. These slots are disposed at aconstant distance from the axis 43 of the differential, and extendparallel to that axis. A central ring member 56 closes the radiallyinner ends of the slots and completes the guide surfaces. The blocks,which reciprocate in the slots 55, are complementary in shape to theseslots along the three sides of the slots, and are arcuate in shape attheir radially inner ends to fit the ring 56.

Driving members, such as shown at 31' and 31 in Figs. 3 and 4,respectively, may be used in place of the driving member 31 (Fig. 1) ifdesired, in all embodiments of the invention herein described.

Fig. 5 illustrates diagrammatically the preferred motion of the slidingblocks. The horizontal line, or abscissa 57 represents the relativeturning angle of the side members 50, 51 of the differential. Thevertical direction or ordinate of the composite curve 58 represents thedisplacement of a sliding block 42. The composite curve 53 is made up ofdistinctly different parts, such as part (1-1;, part bc, part c-d andpart da between points a and a The .sum of these parts a-b-cda rcp--resents a complete cycle of reciprocation of the block.

It should be noted that the parts ab and c-d are straight. Thissignifies that the motion of the sliding block is in these partsdirectly proportional to the relative turning motion of the sidemembers, that is, in these parts the sliding block moves uniformly uponuniform relative turning motion of the side members. These portions arethe Working portions of the reciprocation cycle. The portions b-c andd-r: represent the reversal portions of the cycle of movement of thesliding blocks.

Theconstant proportion of the movement of the sliding blocks to theturning motion of the side members during the working portions of thecycle permits the use of helical surfaces on the sliding blocks and sidemembers that have surface contact with each other, re sulting in lowsurface stresses.

While the reversal portions b-c and da occupy a smaller horizontaldistance than the working portions ab, cd, they occupy a definite partof the total cycle, and are preferably at least half as large as theWorking portions. That. is, the reversal portions 1J-(', d-a occupy atleast half as much relative turning angle as the working portions a-b,c-d of the side members. This is to make for smooth operation, withoutabrupt changes of motion.

Fig. 6 affords an end view of the teeth 48 of a side member 50 and atooth of a sliding block 52, when the teeth of the block and of the sidemember are straight radial teeth. The view is from the outside lookingtoward the axis 43 of the coaxial members. Points a, b, c, of theprofile 60 at the outer ends of the teeth of the side member 50correspond, respectively, to the points a, b, c of the motion diagram ofFig. 5. Points a, b, c" of the profile 61 at the inner end of the teethof the side member 50 correspond, respectively, to points a, b, c, ofthe outer profile, and to points a, b, c of the motion diagram. Theportion n'a-b'b" of the side surface of tooth 48 of member 50 is ahelical surface of constant lead. it is matched to the depth ofengagement by a counterpart helical surface of constant lead provided onthe tooth 46. This tooth is shown in engagement with a portion of thearea ar1l2b in surface contact.

The outerand inner profiles 60, 61 of the tooth surface of the tooth 48lie in cylindrical surfaces coaxial with the axis 43 of thedifferential. When the cylindrical surfaces of these profiles and ofintermediate profiles are developed into a plane, their, profiles ha ethe same extent in the axial,"or vertical, direction, but occupydifferent distances in the peripheral, or horizontal, direction. ,Thevarious profiles differ from each other, but can be derived from theouter profile by contracting its horizontal scale. This applies to theteeth 46 of the sliding block as well as to the teeth 48 of the sidemember 50, and to the teeth 47, 49 on the opposite side of the slidingblock and on the opposite side member 51.

It should also be noted that the concave arcuate portion 62 at the toothbottom extends through a peripheral distance at least twice as large asthe convex arcuate portion 63 at the tooth top. The teeth 46 of theblocks 42 have this same characteristic. Thus, in the position ofclosest approach of the sliding blocks to side member 50 (Fig. 8) onlythe arcuate portions 64 of the teeth 46 and the arcuate bottoms 62 ofthe tooth spaces of the side member 50 are in contact, while the sidesof the teeth of these members are separated from each other.

The variation in the profiles lengthwise of the teeth presentsdifficulties to efficient and accurate manufacture. One possible way ofavoiding such difiiculties is to provide teeth or projections on thesliding blocks, each of whose tooth sides is a single simple surface ofrevolution adapted to contact a mating tooth surface of a side member.Such a surface may be completely described by a rotary tool.

Convex spherical surfaces, or convex cylindrical or conical surfaces,are such known surfaces, some of which have been used in connection withside members for differentials such as disclosed. The ribbed orundulatory contact surfaces of the side members can then be produced bygeneration with a rotary tool that describes such a surface ofrevolution of a sliding block. As the tool rotates on its axis, the sidemember to be cut is turned slowly on its axis, and the tool is advancedaxially, as if the sliding block would engage and mesh with the sidemember.

While this procedure solves the manufacturing problems, the contactbetween the sliding block and the guide member is far less intimate thanwith the structure here proposed. Also, surface contact is impossible.The surfaces are stressed severely in operation, causing wear.

It has also been proposed to leave out the arcuate portions 62, 63,entirely, and let the opposed helical surfaces of the teeth come to asharp radial edge. This causes very abrupt reversal of the sliding blockmotion with extreme accelerations, and knocks. Also, this proposalsolves only a part of the manufacturing problems, for according to theknown practices, the helical surfaces with their change in profileinclination along the teeth still present obstacles to eflicientmanufacture.

The manufacturing problems and other problems are solved by the presentinvention by using spirally arranged teeth 48, 46 (Fig. 7) on the teeth,and particularly by providing teeth that extend lengthwise alonginvolute curves. Their end profiles may be the same as the end profilesof the straight teeth 48, 46 of Fig. 6. Likewise, the profiles in theintermediate cylindrical sections coaxial with the differential may bethe same.

In the preferred embodiment of the present invention, then, the sidesurfaces of the teeth of both the blocks and the side members arehelical surfaces of constant lead joined by rounded tips and by roundedtooth bottoms, and the rounded tooth bottoms have an angular width atleast half as large as the angular width of the side surfaces of theteeth, and at least twice as large as the angular width of the tips orouter profiles of the teeth.

In Figs. 9 to 12, the tips 63 of the teeth are shown in heavy lines andthe tooth bottoms 62 in finer lines. The teeth 48 of the side member 50extend along involutes 68 of a circle 67 concentric with the side member50 and coaxial with axis 43. Two such involutes 68 are shown extendedbeyond the region of the teeth in Fig. 9 to show them up more clearly.The top ends 63, as well as the bottoms 62, are all involutes of thebase circle 67. Moreover, all planes perpendicular to the axis of theside member 50 within the tooth region intersect the teeth in involutesof the same base circle.

As known, all tangents to the base circle 67, like the tangent 70, areperpendicular to all the involutes they intersect. They are normals ofthe involutes.

An involute can be considered described by a point of a string' that isunwrapped from the base circle. The point of contact 71 of the string ortangent 70 with the base circle 67 is the curvature center of theinvolute at the considered point of the involute. Involutes have aconstant normal pitch. That is, any two involutes have a constantdistance from each other all along their length. An important feature isthat the normal distances between the adjacent tooth tops 63 is constantalong the length of the teeth, see Fig. 14, which is a normal sectionthrough the teeth, a section along the tangent 70. The composite profile73 of a tooth space is constant in all normal sections along the teeth,while it is only the profiles in cylindrical sections coaxial with theaxis 43 of the side member that change. This removes the chiefmanufacturing difficulty, as will be described further later.

The involute helicoid of constant lead contains a straight sided profilein normal section. Thus, the working portions 72 of profile 73 (Figs. 14to 19) are straight, and have a constant inclination to the axis 43 ofthe difierential. The arcuate connecting portions 62, 63 serve for thereversal of the motion of the sliding blocks, and are in contact duringsuch reversal. They are preferably made circular arcs. The radius of theconcave arc 62 is at least twice as large as the radius of the convexare 63.

It should be understood that in place of exact involutes, approximationmay also be used, to achieve at least a good part of the effect. Forinstance, an involute 63 might be replaced by a circular arc centered atthe curvature center 71 of the involute; and the side surface of a tooth48, might, therefore, be a surface of revolution, of which the straightsided working portion is part of a conical surface.

The use of spiral, or spirally arranged, teeth, in accordance with theinvention, achieves a further important advantage. It reduces the endthrust required to achieve a given internal braking or locking effect.This is shown diagrammatically in Fig. 18, which is a section coaxialwith axis 43 taken midway through a spiral tooth 48'. Point 74 denotesthe mean point of tooth engagement in the region shown. If the frictionis zero, the pressure exerted upon the tooth would be perpendicular tothe tooth surface. It would be in thedirection of the tooth surfacenormal 75 shown in projection in Fig. 18, and at right angles to theprofile 76 of the tooth in this section. The normal 75 is inclined tothe drawing plane increasingly with increasing spiral angle of theteeth. It would lie in the drawing plane only if the tooth werestraight.

Only the peripheral component 77-74 of the tooth pressure producestorque. On straight teeth, the normal tooth pressure at zero frictionand with a given peripheral components 77-74 would be measured by thedistance 78-74. With spiral teeth, however, the normal tooth pressure islarger. Distance 7374 represents only its projection to the drawingplane. Thus, if the inclination of the surface normal to the drawingplane were 45, or 60, the normal pressure would be represented by thedistance 78-74 divided by cos 45 or cos 60, respectively. It wouldamount to 1.41 times or twice, respectively, the normal pressure onstraight teeth.

The frictional force that opposes relative sliding of the contactingteeth of the profile 76 increases with increasing normal pressure, aboutin the same proportion as said pressure, while the axial thrustcomponent of the normal tooth load remains the same. This thrustcomponent is represented by distance 77-78 that extends in the directionof the axis of the differential.

Depending on the direction of sliding, tooth loads result that areinclined to the direction of the normal 75,

teeth 46'.

.axis 43 of the coaxial members of the differential.

The spiral teeth 48, 49 (Figs. 9 and 10) of the side members 50, 51 areof opposite hand, in accordance with the invention, the teeth on onemember being of right hand and'the teeth are on the other member of lefthand. Likewise, oppositeends of the sliding blocks 42 have teeth ofopposite hand (Figs. 11 and 12).

The hand is defined by looking at the toothed ends. If the teeth of bothsides of a sliding block are visualized as looked at in the samedirection, however, one side from the front and the other side from therear, the hand of the teeth would appear to be the same. Thus, whenlooked at in Fig. 11 the teeth 47' (Fig. 12) of the sliding block 421would appear to coincide with the teeth 46' of that sliding block. Thismeans that the normal forces exerted on the tooth surfaces at the frontand rear of each sliding block lie approximately in a plane. The blocksare Well mounted in theirguide surfaces since there are no appreciablemoments tending to tip the blocks.

Fig. 11 shows the teeth 46 of the blocks 42 that engage the teeth 48' ofthe side member 50 (Fig. 9). Fig. 12 shows the teeth 47 of the blocks 42that engage the teeth 49' of the side member 51 (Fig. 10). The teeth arepreferably chamfered at their acute ends, wherever necessary. Thus, inFigs. 9 and 10, 81, 82 indicate the chamfered portions at the outer andinner ends of the teeth.

Fig. 13 illustrates a modification of the invention in which the slidingblocks 42a have cylindrical outside surfaces 84 with areuate recesses85. A central member 86 then retains the blocks in their proper radialpositions.

The end of a sliding block contains preferably more than a single tooth.Thus, the blocks 42 all contain two These teeth are disposed alike onone end of all the blocks. On the opposite ends of the sliding blocks42, the teeth 47 are arranged in two different patterns. The teeth 47 ofthe blocks 421, 423, 425 and 427 are identically disposed. Each blockhas two teeth. The teeth of blocks 422, 424, 426, 428 are identicallyarranged, but in a different way from the teeth of blocks 421, 423, 425and 427. Each of the blocks 422, 424, 426, 423 has three teeth. Theteeth 47' themselves on all the blocks are identical, but the blocks422, 424, 426, 428 have teeth in the places Where the blocks 421, 423,425, 427 have tooth spaces. In other words, the teeth of alternateblocks are turned through half a pitch about the axis of thedifferential. A tooth on one end of a block is aligned with a toothspace on the other end of the block in the ease of the blocks 422, 424,426 and 428.

The reason for this arrangement will be apparent from Fig. 15, whichapplies to spiral teeth and to straight teeth alike. It is a developmentto a plane of a part of the periphery of the tooth zones. The distancebetween the two dash and dot lines 83, 83 represents half thecircumference. In the instance illustrated, both side members 50, 51have fourteen teeth, that is, seven per half circumference. There areeight sliding blocks 42, all uniformly spaced and at equal distancesfrom the axis of the differential. The tooth profiles of the two sidemembers are identical and correspond to Figs. 6 and 7. Any two slidingblocks that are half the circumference apart are identical, and are inthe same con- -metrally opposite :block-428 are in the middle of theopposite reversal.

When the side members 50, 51 turn relative to each other, the blocksreciprocate, each at the rate indicated in the diagram of Fig.5. Theykeep their phase differences, adjacent blocksstaying apart a quarter ofa complete reciprocation cycle.

It is seen thatthere are asufiicient number of phase differences toprovide continuous action, even though all the sliding blocks havethesame distance from the axis of the differential and are all evenlyspaced, While the two side members 50, 51 have the same number of teeth.Moreover, there are onlytwo groups of sliding blocks, four blocks ineach group, whose tooth position differs only on one end of the blocks.

Other tooth members than fourteen can be used on the side members, andother numbers of blocks can also be employed. Preferably, however, Ikeep the tooth number of the side members at double an uneven number,and the numberofblocks at eight. With each block containing a pluralityof teeth, a differential of great strength is achieved; and thesurfacestresses are kept low.

The arrangement indicated in Fig. 16 differs from that of Fig. 15 merelyby the positions of the teeth on the ends of thesliding blocks. Theblocks 42 have teeth. where the blocks 42 have tooth spaces, and toothspaces where the blocks 42 have teeth. The blocks 42' also arearranged,-however, in two'groups of four blocks each, the blocks ofonegroup alternating with the blocks of the other.

In the arrangement of Fig. 16, the sliding blocks 4212 are all alike. Toachieve phase differences in the action of the blocks, the tooth numbersof the two side members 5012 and 51b are different. In the instanceillustrated these side members have fourteen and sixteen teeth,respectively. .Here, ten blocks 42b are used. The number of blocksshould be equal to the sum of the teeth of the side members, or anintegral fraction thereof, in this embodiment of the invention. While,in this embodiment, the blocks are shown with a single tooth on eachend, they may also be provided with a plurality of teeth. The profileinclination of the teeth of the two side members b, 51b depends on thetooth number, and differs on the two members, as is readily understood.The torque transmitted to the two side members would be in proportion totheir tooth numbers at zero friction. Friction provides a range oftorque proportions.

The arrangements shown in Figs. 15, 16 and 17 are for transmitting aboutequal overall torques to both driven members. On inter-axledifferentials it is sometimes desirable to transmit unequal torque tothe two driven members. In this case, the tooth numbers of the two sidemembers should be altered. When the driver carries the sliding blocksthe tooth numbers of the driven members should be approximately in theproportion of the torque to be transmitted to them. The arrangement ofFig. 17 is especially suitable for this case, when the difference intooth numbers is large.

It is also possible to have one of the side members as the driver, theside member with larger number of teeth according to the principlesdisclosed in my patent No. 2,790,334, April 30, 1957.

From the preceding description it will be seen that surface contact isattained between the side members and the blocks, and that the blockmotion is at a constant proportion to the turning motion of each sidemember 9 during the working contact and that there is a definitereversal period for the blocks to reverse their motions.

A particularly smooth operation of the differential is attained when thecoefficient of static friction and the coefficient of sliding frictionare nearly equal. Ordinarily, the coeflicient is larger for staticfriction than for sliding friction depending upon the materials incontact. However, materials may be so selected that the difierence issmall. Such materials generally do not have the strength of hardenedalloy steel. One such known material is graphite composition.

With the present invention, the use of materials of less strength andimproved frictional properties is feasible, be-' cause the surfacecontact provided results in relatively low stresses. This is indicatedin Fig. 19, which is a fragmentary normal section taken at right anglesto the spiral teeth 48" of a side member. The teeth are faced with amaterial 87 of improved frictional properties. Preferably, the matingteeth are made of a single material only and have no facing. The facingmay be applied to the teeth of the side members, or, if desired, to theteeth of the sliding blocks instead. Plating may also be used instead offacing, if desired.

A principal way of producing the spiral teeth is by cutting. Fig. 20illustrates one way of cutting the teeth. The teeth of the side member50 are here shown in normal section as in Fig. 14. The tool is indicatedat 83. It has an axle 89 lying in the sectional plane of the teeth andmay be a milling cutter or a grinding tool. The cutter 88 has aplurality of ring shaped cutting surfaces 92 whose cutting edges, orworking portions, lie in surfaces of revolution 90, 91 whose profilesmatch the sectional profiles of the teeth. As the tool rotates on itsaxis, the known feeding motions are provided to produce involute spiralteeth, namely, the workpiece 50 is slowly turned on its axis 43 whilethe tool 88 is fed in the direction of the tangent 70 (Fig. 9) to thebase circle of the involute. This straight line feed is timed with theturning motion of the workpiece so that the feed velocity is equal tothe peripheral velocity of the workpiece at the base circle 67. Thecycle is repeated for different teeth.

Instead of using a cutter such as shown at 88 in Fig. 20,

a simpler cutter or grinding wheel with a single ring shaped surface maybe used such as that of one of the discs 92 of the multiple disc cutter88. The feed is then made long enough so that this single disc willcover completely the whole length of the teeth of the side member 50 tobe cut.

Another way of cutting the teeth is with a form tool 93, such as shownin Fig. 21. Here the tool has a cutting motion in the direction of thetangent 70, the tool being reciprocated at a uniform rate in thedirection of this line, the tool moving along the line on its cuttingstroke, and being clapped out of engagement with the work at the end ofthe cutting stroke and returned, while clear of the work, in theopposite direction, the work rotating continuously on its axis at auniform rate, so that the too-l 93 describes the whole length of a toothspace on each stroke. A complete tool stroke, cutting and return, withthe tool 93, should occur in the time that it takes for the workpiece toturn through an integral number of teeth or pitches, which number shouldbe prime to the tooth number of the workpiece. Since the workpiececontinues to turn in the same direction during the return strokes of thetool, as during the cutting strokes, the tool engages different toothspaces on successive cutting strokes. An additional motion for indexingof the work is, therefore, unnecessary. The cut starts at the tops ofthe teeth; and the work is gradually fed into the tool along its axis43, until full cutting depth is reached. The teeth are completedsuccessively on the last cutting strokes in each tooth space, that is,are completed in the last feed position of the work.

Of course, tools with multiple cutting teeth may be also used. Also, aplurality of tools may be used to speed up production further. Thesewould be spaced about the work axis and cut from different sides, alonglines tangent to the base circle of the involute. They would preferablycut simultaneously, and have simultaneous return strokes. At the end ofa cutting stroke, the workpiece wouldmove back along its axis, to clearthe tools during the return stroke. At the end of the return stroke, theworkpiece moves up to cutting position again. This is a very efficientcutting process.

Figs. 22 and 23 illustrate a further way of cutting the spiral teeth ofthe side members, and also those of the sliding blocks. The latter areset up in chucks or holders at such a spacing that their teeth are partof the teeth of a complete gear. Here a gear type cutter 95' is usedthat has a conical cutting face 96. Its axis is at 97 inclined to theface of the workpiece 50 so that cutting clearance is obtained for thecutter teeth 98, which extend parallel to the cutter axis 97. Thecutting edges 99 then remain at the same distance from the cutter axisafter sharpening during the whole life of the cutter. The cutting edgesof the teeth are shaped conjugate to the rack profile of the sectionshown in Fig. 22.

In operation, using tool 95, the workpiece 50 and the cutter 95 arerotated on their respective axes 43, 97 at the inverse proportion oftheir tooth numbers. The cut starts with the cutter 95 adjacent one endof the teeth of the workpiece. A relative feed motion is added, in whichthe butter in effect rolls along the line 70, that is tangent to thebase circle of the involute teeth being produced. In this way, the teethare cut in a continuous operation.

Among other methods, which may be employed for cutting the teeth of theside members and of the sliding blocks, it is also possible to use ataper hob of contour similar to that of milling cutter 88 of Fig. 20,and having a single thread of several convolutions.

It will be seen, then, that the desired involute spiral teeth can beproduced eificiently and accurately, and in 'many ways.

While the invention has been described in connection with severaldifferent embodiments thereof, then, it will be understood that it iscapable of further modification, and this application is intended tocover any variations, uses, or adaptations of the invention following,in general, the principles of the invention and including such departures from the present disclosure as come within known or customarypractice in the art to which the invention pertains, and as fall withinthe scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

l. A differential comprising three coaxial and relatively rotatablemembers, of which one is the driver and the two other members are drivenmembers adapted to transmit torque, one of said members being disposedbetween the other two members, a plurality of sliding blocks beingmounted on said one member for reciprocatory motion in the direction ofthe axis of said members, each of said blocks having teeth at itsopposite ends, said other members being provided with teeth on the sidesthereof facing the opposite ends, respectively, of the sliding blocksfor engagement with the teeth of the sliding blocks, the teeth of saidblocks and of said other members having helical side surfaces ofconstant lead that have profile inclinations increasing with increasingdistance from the axis of said members in cylindrical sections coaxialwith said members, the opposite helical side surfaces of adjacent teethof the blocks and of the two other members being joined by arcuateportions, the arcuate portions of mating teeth being disposed to engageeach other, thereby to provide for reversal of the sliding blocksadjacent the position of closest axial approach of the teeth of theblocks and said other members, and while the helical surfaces of saidteeth are out of engagement with each other.

2. A differential comprising three coaxial and relatively rotatablemembers, of which one is the driver and the two other members are drivenmembers adapted to transmit torque, the said driver being disposedbetween said other two members, sliding blocks mounted-on said driverfor reciprocatory motion in the direction of the axis of said members,each of said sliding blocks having teeth at its opposite ends,each-ofsaid other members having teeth on the side thereoffacing one endof the sliding blocks for engagement with the teeth provided on thesliding blocks, the profiles of the teeth of the sliding blocks changingalong the length of the teeth in cylindrical sections coaxial with saidmembers, said profiles being composed of approximately straight portionsand of arcuate portions, the teeth of said other two members havingarcuate portions adapted to engage the arcuate portions of the teeth ofsaid blocks to effect reversal of the motion of the blocks.

3. A differential comprising three coaxial and relatively rotatablemembers, of which one is the driver and the other two members are drivenmembers adapted to transmit torque, said driver being disposed betweenthe other two members, and having a plurality of ways extending in thedirection of its axis, a plurality of sliding blocks mounted in saidways for reciprocation therein between said other two members, a centralmember disposed radially inwardly of said blocks to retain said blocksin said Ways, each of said sliding blocks having teeth on its oppositeends, said other two members'having teeth on the sides thereof facingthe ends of the sliding blocks, respectively, for engagement with theteeth of' the sliding blocks, the teeth of said other two members and ofsaid blocks being shaped to effect reciprocation cycles of the blockscomposed of a uniform motion portion in each direction and of reversalportions, said sliding blocks being arranged in two groups, the blocksof one group alternating with the blocks of the other around the axis ofsaid members, all of said blocks being disposed at the same distancefrom said axis, the blocks of the two groups having the teethdifferently disposed on one end of said blocks.

4. A differential comprising three coaxial and relatively rotatablemembers, of which one is the driver and the two other members are drivenmembers adapted to transmit torque, said driver being disposed betweensaid other two members, a plurality of sliding blocks'mounted on saiddriver for reciprocatory motion in the direction of the axis of saidmembers, each of said blocks having teeth at its opposite ends, each ofsaid other two-members having teeth on its sidefacing one 'end of thesliding blocks for engagement with the teeth on said sliding blocks, the

teeth on said sliding blocks and of said other two members havinghelical side surfaces joined by arcuateportions, the arcuate portions atthe tooth bottoms being at least half as large as the helical sideportions.

5. A differential comprising three coaxial and relatively rotatablemembers, of which one is the driver'and the other two are driven membersadapted to transmit torque, said driver being disposed between said twoother members and having a plurality of ways which extend in thedirection of its axis at equal distances therefrom and which havecircular arcuate profiles, a plurality'of sliding blocks mounted in saidways for reciprocation therein between said othertwo members, a centralmember disposed radially inwardly of said blocks for retaining saidblocks in said ways, each of said blocks having teeth at its oppositeends, said other two members having teeth on the sides thereof facingthe opposite ends, respectively, of said blocks for engagement with theteeth provided on said blocks, the teeth of said other two members andof said blocks having helical side surfaces of constant lead and havingarcuate portions connecting said helical side surfaces, the toothnumbers of said other two members being equal and being double anunevennumber, and said sliding blocks being arranged in two groups, the blocksof one group alternating with the other about the axis of said members,the blocks of the two groups having teeth differently arranged on oneend thereof.

6. A differential comprising three coaxial and relatively rotatablemembers, one of which is the driver and the 12 other two of which aredriven members adapted to transmit torque, a plurality of sliding blocksmounted on one of said members for reciprocatory motion in the directionof the axis of said members,-'-each of said blocks having spirallyarranged teeth OnwitsOPPOSite ends, said other two membershaving-spirally arranged teeth on the sides thereof facing the oppositeends, respectively, of said sliding blocks for engagement of the teethof said sliding of said sliding blocks for engagement with the teeth of'said sliding blocks, to reciprocate said sliding blocks on relativerotation of said other two members, the teeth of said other two membersbeing spirally arranged and.

being of opposite hand.

8. A differential according to claim 6 in which the teeth extendlongitudinally, at least approximately, along involutes of a circleconcentric with the axis of said members.

9. A differential according to claim 8, in which the interdental spacesof said spirally arranged teeth have a constant composite profile allalong their lengths in normal sections perpendicular to the longitudinaldirection of said spaces, said profiles being composed of workingportions and of curved portions controlling the reversal of the slidingblock motion.

10. A differential according to claim 9, in which the working portionsof the tooth profiles are straight and inclined to the direction of theaxis of the three members.

11. A differential according to claim 9, in which the Working portionsof the tooth profiles are inclined to the direction of the axis of saidmembers at a constant angle less than 45.

12. A differential according to claim 7, in which the spirally arrangedteeth extend longitudinally, at least approximately, along involutes ofa circle concentric with the axis of said members, said circle being ofthe same diameter on said other two members.

13. A differential according to claim 7, in which the profiles of theteeth of said other two members contain working portions and curvedreversal portions, the wori1- ing portions of the profiles beinginclined to the direction of the axis of said members at angles smallerthan 45 in normal sections perpendicular to the direction of the teeth'14. A differential according to claim 9 in which said curved toothprofile portions are circular arcs, the tops of the teeth being ofconvex arcuate shape, and the bottoms of the tooth spaces being ofconcave arcuatc shape, the radius of the concave arcs being larger thanthe radius of the convex arcs.

15. A differential according to claim 6 in which the working portions ofthe teeth of the sliding blocks engage the working portions of the teethof said other two members with surface contact, the teeth of one of saidmembers being faced with a material different from the material of thebody of said teeth and of superior frictional properties.

16. A differential comprising three coaxial and relatively rotatablemembers, one of which is the driver and the other two are driven membersadapted to transmit torque, a plurality of sliding blmks mounted on oneof said members between the other two for reciprocatory movement in thedirection of the axis of said members, each of said sliding blockshaving spirally arranged teeth 13 at its two opposite ends, the hand ofsaid teeth being opposite at said two ends.

17. A differential comprising three coaxial and relatively rotatablemembers, of which one is the driver and the other two are driven membersadapted to transmit torque, a plurality of sliding blocks mounted on oneof said members between the other two members for reciprocatory motionin the direction of the axis of said members, each of said slidingblocks having spirally arranged teeth at its two opposite ends, the handof said teeth being opposite at the two ends, and said teeth extendingalong involutes of a circle concentric with the axis of said members.

18. A differential according to claim 16 in which a tooth at one end ofa sliding block is aligned with a tooth space at the other end of theblock.

19. A differential comprising three coaxial and relatively rotatablemembers, of which one is the driver and the other two members are drivenmembers adapted to transmit torque, a plurality of sliding blocksmounted on one of said members between the other two members forreciprocatory motion in the direction of the axis of said members, eachof said sliding blocks having teeth at its opposite ends, said other twomembers having teeth on the sides thereof facing the teeth of saidblocks, respectively, the teeth of said blocks and of said other twomembers being, at least, approximately of involute lengthwise curvatureand having side portions of straight profile, the tops of said teethbeing of convex arcuate curvature, and the bottoms of the spaces betweensaid teeth being of concave arcuate curvature and of greater radius thanthe tops of the teeth.

20. A differential comprising three coaxial and relatively rotatablemembers, of which one is the driver and the other two members are drivenmembers adapted to transmit torque, a plurality of sliding blocksmounted on one of said members between the other two members forreciprocatory motion in the direction of the axis of said members, eachof said sliding blocks having teeth at its opposite ends, each of saidother two members having teeth on its side facing confronting oppositeends of the sliding blocks, respectively, for engagement with the teethon said sliding blocks, the teeth on said sliding blocks and on saidother two members being longitudinally curved and having helical sidesurfaces.

21. A differential according to claim 20 in which opposite sides of theteeth are connected both at top and bottom by arcuate portions, and inwhich the angular width of the bottom connecting portions at any givenradial distance from the axis of a member is at least twice as large asthe angular width of the top connecting portions at the same radialdistance from the axis of said member. 3;

'22. A differential according to claim .20 in which the opposite sidesof the teeth are connected both at top and bottom by arcuate portions,and in which the angular width of the bottom connecting portions of theteeth at any radial distance from the axis of a member is at least halfas large as the angular width of the helical side portions of the teethof said member at said radial distance.

23. A differential having three coaxial and relatively rotatablemembers, one of said members being the driving member, the two other ofsaid members being driven members connected respectively to two axleshafts, said other members having spiral teeth provided on the sidesfacing towards each other, a part slidable in said driving member in thedirection of the axis of said members, said part having at opposite endsthereof teeth adapted to engage the teeth provided on said other twomembers to effect driving engagement therewith, the teeth of said twoother members being of opposite hand and of at least approximateinvolute lengthwise curvature.

References Cited in the file of this patent UNITED STATES PATENTS1,897,555 Ford Feb. 14, 1933 FOREIGN PATENTS 431,020 Great Britain June28, 1935 537,974 Great Britain July 16, 1941

